Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$94.33	5.183%	$99.2191	$99.22	$99.20	$99.20
Purchase #2	$48.72	10.628%	$53.898	$53.90	$53.90	$53.90
Purchase #3	$145.52	8.592%	$158.0231	$158.02	$158.00	$158.00
Purchase #4	$17.86	13.457%	$20.2634	$20.26	$20.25	$20.30
Purchase #5	$125.96	9.648%	$138.1126	$138.11	$138.10	$138.10
Purchase #6	$71.80	8.700%	$78.0466	$78.05	$78.05	$78.00
Purchase #7	$220.35	13.391%	$249.8571	$249.86	$249.85	$249.90
7 purchase totals =	$724.54		$797.4199	$797.42	$797.35	$797.40